Hey ho, I have used the Metabones Speed Booster with a Canon 200mm f2.0 hand held in indoor light. Is doable even if the lens is reasonably large. But the dof at an effective fixed telephoto equivalent of about 213mm f1.4 is pretty narrow. The choir was only focusable row by row and I am not sure that all eyes and noses were in focus at the same time either (grin).